Boiler



FIG. 1 is a perspective view of a boiler according to my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a left side elevational view thereof;

FIG. 4 is a right side elevational view thereof;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a bottom plan view thereof.

In the drawings, the broken lines depict unclaimed subject matter only and form no part of the claimed design. 

CLAIM The ornamental design for a boiler, as shown and described. 